Composite Nanocrystalline/Amorphous Thin Films for Particle Detector Applications
- PDF / 225,059 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 9 Downloads / 256 Views
Composite Nanocrystalline/Amorphous Thin Films for Particle Detector Applications Zvie Razieli, Roger Rusack, and James Kakalios Department of Physics and Astronomy, University of Minnesota, Minneapolis, MN, 55455, U.S.A. ABSTRACT Thin films of amorphous silicon with nanocrystalline silicon inclusions are fabricated using a dual plasma PECVD co-deposition system. Raman spectroscopy and X-ray diffraction confirmed the crystallinity of the embedded nanocrystals as well as their diameter, which is varied from 4.3 nm to 17.5 nm. The dark conductivity of the films is highly dependent on the crystal fraction, with a maximum room temperature conductivity found for a crystal concentration of 5.5%, well below the percolation threshold. Proton irradiation at energies of 217 MeV with a total fluence of 5 x1012 protons/cm2 caused no significant radiation damage. The enhancement of the conductivity, along with the absence of radiation damage suggests this material may be a candidate for use in the next generation of particle detectors in the Compact Muon Solenoid in the Large Hadron Collider at CERN. INTRODUCTION The proposed upgrades to the Large Hadron Collider at CERN will lead to average luminosities of ~5×1034 Hz/cm2, and an expected total integrated dose (TID) approaching 1016 hadrons/cm2 at the inner region of the particle tracker. These levels are unprecedented in highenergy physics, and will exceed levels that are compatible with the operation of conventional crystalline silicon-based detectors [1]. There is consequently an active search for materials that can function after these TIDs. One candidate material, hydrogenated amorphous silicon (a-Si:H), has been studied for applications in high radiation environments for many years as it is can be manufactured over large areas at low-cost, and because the signal is stable under intense radiation [2-4]. The main drawbacks of a-Si:H, and the reasons why it has not been adopted by the high-energy physics community, are that the detector thickness is limited to < 50 μm, and the signals are small, with 4.8 – 6 eV required to create an electron-hole (e-h) pair, (in contrast, the energy required for crystalline-Silicon (c-Si) is 3.6 eV). In addition, the Charge Collection Efficiency (CEE) is typically ~ 75% in c-Si based p-i-n detectors, whereas values of 40% or less have been reported for a-Si:H diodes [5] due to the presence of deep traps. Following progress in understanding the benefits of defect engineering and cooling in high radiation environments, c-Si has remained the detector material of choice of tracking detectors. However, the use of c-Si for TIDs above 1015 is problematic due to a significantly reduced CEE caused by the production of deep traps, motivating the invention of novel diode geometries that minimize the collection distance [3]. One exciting recent development in the production of thin-film silicon involves the inclusion of silicon nanocrystals into a-Si:H, which significantly improves the electronic properties of the material. Previous studies have found th
Data Loading...
